Linux Foundation Secure Boot support released - what does it mean?
The UEFI bootloader that the Linux Foundation have been working on has just been released. That means we now have two signed bootloaders available - this one and shim.
Samsung laptop bug is not Linux specific
I bricked a Samsung laptop today. Unlike most of the reported cases of Samsung laptops refusing to boot, I never booted Linux on it - all experimentation was performed under Windows. It seems that the bug we've been seeing is simultaneously simpler in some ways and more complicated in others than we'd previously realised.
So, some background. The original belief was that the samsung-laptop driver was doing something that caused the system to stop working. This driver was coded to a Samsung specification in order to support certain laptop features that weren't accessible via any standardised mechanism. It works by searching a specific area of memory for a Samsung-specific signature. If it finds it, it follows a pointer to a table that contains various magic values that need to be written in order to trigger some system management code that actually performs the requested change. This is unusual in this day and age, but not unique. The problem is that the magic signature is still present on UEFI systems, but attempting to use the data contained in the table causes problems.
We're not quite sure what those problems are yet. Originally we assumed that the magic values we wrote were causing the problem, so the samsung-laptop driver was patched to disable it on UEFI systems. Unfortunately, this doesn't actually fix the problem - it just avoids the easiest way of triggering it. It turns out that it wasn't the writes that caused the problem, it was what happened next. Performing the writes triggered a hardware error of some description. The Linux kernel caught and logged this. In the old days, people would often never see these logs - the system would then be frozen and it would be impossible to access the hard drive, so they never got written to disk. There's code in the kernel to make this easier on UEFI systems. Whenever a severe error is encountered, the kernel copies recent messages to the UEFI variable storage space. They're then available to userspace after a reboot, allowing more accurate diagnostics of what caused the crash.
That crash dump takes about 10K of UEFI storage space. Microsoft require that Windows 8 systems have at least 64K of storage space available. We only keep one crash dump - if the system crashes again it'll simply overwrite the existing one rather than creating another. This is all completely compatible with the UEFI specification, and Apple actually do something very similar on their hardware. Unfortunately, it turns out that some Samsung laptops will fail to boot if too much of the variable storage space is used. We don't know what "too much" is yet, but writing a bunch of variables from Windows is enough to trigger it. I put some sample code here - it writes out 36 variables each containing a kilobyte of random data. I ran this as an administrator under Windows and then rebooted the system. It never came back.
This is pretty obviously a firmware bug. Writing UEFI variables is expressly permitted by the specification, and there should never be a situation in which an OS can fill the variable store in such a way that the firmware refuses to boot the system. We've seen similar bugs in Intel's reference code in the past, but they were all fixed early last year. For now the safest thing to do is not to use UEFI on any Samsung laptops. Unfortunately, if you're using Windows, that'll require you to reinstall it from scratch. comments
The Samsung laptop issue is not fixed
The recent Linux kernel commits avoid one mechanism by which Samsung laptops can be bricked, but the information we now have indicates that there are other ways of triggering this. It also seems likely that it's possible for a userspace application to cause the same problem under Windows. We're still trying to figure out the full details, but until then you're safest ensuring that you're using BIOS mode on Samsung laptops no matter which operating system you're running. comments
Don't like Secure Boot? Don't buy a Chromebook.
People are, unsurprisingly, upset that Microsoft have imposed UEFI Secure Boot on the x86 market. A situation in which one company gets to determine which software will boot on systems by default is obviously open to abuse. What's more surprising is that many of the people who are upset about this are completely fine with encouraging people to buy Chromebooks.
Out of the box, Chromebooks are even more locked down than Windows 8 machines. The Chromebook firmware validates the kernel, and the kernel verifies the filesystem. Want to run a version of Chrome you've built yourself? Denied. Thankfully, Google have provided a way around this - you can flip a physical switch hidden somewhere in the machine to disable the validation. Doing so deletes all your data in the process, in order to avoid the situation where a physically present attacker wants to steal your data or backdoor your system unnoticed, but after that it'll boot any OS you want. The downside is that you've lost the security that you previously had. If a remote attacker manages to replace your kernel with a backdoored one, the firmware will boot it anyway. Want the same level of security as the stock firmware? You can't. There's no way for you to install your own signing keys, and Google won't sign third party binaries. Chromebooks are either secure and running Google's software, or insecure and running your software.
Much like Chromebooks, Windows 8 certified systems are required to permit the user to disable Secure Boot. In contrast to Chromebooks, Windows 8 certified systems are required to permit the user to install their own keys. And, unlike Google, Microsoft will sign alternative operating systems. Windows 8 certified systems provide greater user freedom than Chromebooks.
Some people don't like Secure Boot because they don't trust Microsoft. If you trust Google more, then a Chromebook is a reasonable choice. But some people don't like Secure Boot because they see it as an attack on user freedom, and those people should be willing to criticise Google's stance. Unlike Microsoft, Chromebooks force the user to choose between security and freedom. Nobody should be forced to make that choice. comments
The current state of UEFI and Linux
Executive summary: Most things work fine.
Things we know are broken:
ITWire still has problems with basic accuracy
ITWire ran a story on the 12th of January entitled "Fedora still has problems with secure boot". It ends up discussing two issues with the author's experience with the Fedora installer - that he can't reclaim any free space on existing drives, and that the installer didn't automatically add entries for Windows to the grub menu. These are certainly legitimate issues, and I don't want to suggest that it's reasonable for people to have to manually alter their configuration in order to support dual boot. But they're not issues with Fedora's support for secure boot, despite the enthusiasm with which certain people have jumped on the story. We've received one credible report of a secure boot related problem with Fedora on a couple of Toshiba laptops, which appears (and I want to stress that we're still working on diagnosing it) to be a firmware bug rather than any kind of problem with Fedora.
Mistakes happen in journalism, and sometimes there are differences of opinion. But this story is simply wrong. When asked about it in the comments, the author failed to support his position. When contacted, the editor in chief was willing to add a note saying that I disputed the arguments but was unwilling to remove the incorrect claims. As a result, the internet remains full of links and reposts of an article that unashamedly tells users that the current Linux distribution with the best UEFI hardware support has issues with something it has no issues with.
For reasons that are unclear to me, ITWire seems to have some sort of well regarded status in the Australian technical industry. It seems entirely undeserved. comments
Upcoming conferences
Unfortunately I'm not going to make it to LCA this year, but there's still plenty of UEFI coverage - Dong Wei, Vice President of the UEFI forum, will be giving an introduction to UEFI, and James Bottomley, who's been working on the Linux Foundation's UEFI bootloader solution, will be talking about Secure Boot.
For those of you on this side of the Pacific (or who just can't get enough of listening to my melodious voice), I'll be keynoting the South California Linux Expo next month. This will be a discussion of the more social aspects of our work on Secure Boot over the past year and a half - an epic tail of astonishment, terror, politics, confusion and hard won victories, and the remaining issues that are yet unsolved. Clearly not to be missed. If California's too far for you, then come March I'll be at the North East Linux Fest. I'll be talking about how to make sure that your Linux distribution works with Secure Boot, and, assuming I've got the code finished by then, a little about how to break it. comments
Experiences with depression
I've been lucky in life. I've known several people who've killed themselves, but I've been friendly with them rather than friends with them. Their deaths have saddened me, but haven't left giant gaping holes that I have trouble imagining filling. I've also been lucky in that I'm not especially predisposed towards depression, and even luckier that the one serious episode I had ended well. That luck means I'm not qualified to speak authoritatively on the topic, but this seems like a good time to share.
Most of 2002 wasn't great for me. Many of my friends had graduated and moved away. My PhD, which was what I'd spent the past few years of my life working towards, was going horribly wrong. The girl I liked didn't like me. Lots of individual small things that didn't fundamentally matter, but which build up into overall feelings of isolation and failure at life. I was spending an increasing number of days not leaving bed and not talking to people. It wasn't that I couldn't have fun - socialising was still pleasurable, and I didn't actively avoid people, but it was always tempered with the knowledge that this was temporary and I'd be returning to the unhappiness afterwards. I couldn't see any sequence of events that would turn my life around and restore my happiness. This was how life was, and this was how life was going to be. I'd irrevocably fucked up, and this was my future.
Looking back, what strikes me is how reasonable this seemed. I could point at specific things that were making me unhappy, and nobody could argue that it was unreasonable to be unhappy about them. There wasn't any point in speaking to people about it, because what would they be able to do except agree that I was justifiably unhappy? I thought about suicide. Not seriously, because overall life still seemed worthwhile, but I could conceive of a level of further unhappiness that would make it seem like the best choice. I don't think it would ever have occured to me to speak to someone about it first. It seemed like it would be the same argument - I'm justifiably unhappy, I already feel like I'm letting my friends down, what could they do other than tell me that my feelings are wrong or make me feel even more guilty? So, when I saw exhortions for people to speak to someone if they felt suicidal, it seemed like they were talking to people who hadn't thought this through as well as me. It felt like I'd thought this all through carefully and rationally and come to a completely logical decision. If changes in circumstances and further consideration made it seem like suicide was the better choice, that would be because it was the better choice. Maybe other people weren't thinking about this as logically as I was. Maybe they'd have their minds changed by speaking to a friend or a professional. I wouldn't. Of course, with hindsight I was rationalising the way I already felt rather than making entirely rational decisions. I could have rationalised myself to death even though there were (in my case) straightforward ways to make my life better.
In any case, I've no idea how close I ever got to that point. Things were at their worst in August - by September I had a new job and new house, and things just got better from there. In the end, the friends I was convinced could do nothing for me ended up giving me the opportunity to find gainful employment and made sure I had somewhere to live. Without them, things might have been different. As it was, I spent less than nine months depressed and it was still the most hellish experience of my life. The thought of returning to that state is terrifying. I was lucky. I might not be again.
There's no terribly good moral here. If I'd known more about depression beforehand, I might have been able to identify what was happening to me and seek professional help. Other than that, I didn't learn anything about how to avoid or deal with depression. The experience didn't make me a better person. I've no advice for people in the same situation. The only thing I gained from it all was the realisation that if I'd felt any worse and knew that this was what I faced for the rest of my life, death might not have been the worst choice I had.
Depression is a huge social problem and we deal with it badly. We refuse
to talk about it, and when we do talk about it we mostly limit ourselves
to platitudes about how things will get better or placing the blame on
depressed people for not wanting to talk to those around them. Sometimes
it doesn't get better. Sometimes talking to those around you will make
things worse. People need to be aware of what the effects of depression
are and get better at identifying it in others, rather than assuming
that they'll be able to ask for help themselves. Society as a whole
needs to be better at ensuring that professional support is there for
people who need it. And, unless we can make massive improvements in our
understanding of the causes of depression and effective mechanisms for
countering it, we need to accept that it will cost us friends. Let's
redirect the anger we feel at their choice to avoid a lifetime of misery
into anger at the society that still hasn't done everything it can to
help them. comments
No, Linux won't be easy to run on a Microsoft Surface
The Microsoft Surface is a fairly attractive bit of tablet hardware, and as a result people have shown interest in running Linux on it. The immediate problem is that (like many ARM devices) it has a locked-down firmware that will only run signed binaries - unlike many other ARM devices, this is implemented using an existing standard (UEFI Secure Boot). Microsoft provide a signing service for UEFI binaries, so it's tempting to think that getting around this restriction would be as simple as taking an existing Linux bootloader, signing it and then booting. Unfortunately Microsoft's signing service signs binaries using a different key (the "Microsoft Windows UEFI Driver Publisher" key) to the one used to sign Windows, and the Surface doesn't carry that key. Booting Linux on these devices would involve finding a flaw in the firmware and using that to run arbitrary code.
Could this also be a problem on x86? In theory - Microsoft don't require that vendors carry the driver publisher key, and so a system could be Windows 8 certified and still not carry it. It's unlikely to occur in practice, though, since any third party expansion hardware will then fail on that device. As a result, anything with PCIe or Expresscard slots is effectively certain to have this key. If anyone finds any counterexamples, please let me know. comments
Booting signed versions of Linux on Windows 8 machines
Some people have complained that they can't install Linux on new machines because their firmware won't let them choose a boot device. This is part of Windows 8's fast boot support - the keyboard may not be initialised until after the OS has started. To deal with this, insert the install media and reboot your computer. Wait for Windows 8 to start. While holding down shift, click on the power icon and click on restart. When the menu appears, click "Use a device" and then click your install media. If it's listed more than once, choose the one that says "UEFI" in front of it. Your system will now restart and boot off the install media. comments
New HTML Parser: The long-awaited libxml2 based HTML parser code is live. It needs further work but already handles most markup better than the original parser.
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